<!DOCTYPE html>
<html>
<body>
  <div class="overlay-background" style="position: fixed; width: 300px">
    <div class="sidepanel" id="container" style="position: absolute; height: 300px; overflow: auto;">
      <header class="sticky-header" style="position: sticky; top: 0; left: 0; height: 50px; background-color: blue;">
        sticky header
      </header>
      <div style="height: 500px">
        <p>content to scroll to</p>
        <input type="text" value="input">
        <input type="checkbox" id="vehicle1" name="vehicle1" value="Bike">
      </div>
    </div>
  </div>
</body>
</html>